The present invention relates to polarity testers in electrical circuits, and more particularly to polarity testers for devices providing power outputs through socket means.
Many forms of devices require polarity testing to determine that they have been properly assembled. The present invention is particularly suited for use to test polarity in a device which receives input power through a plug and transmits power through an output socket to an active element. An example of such a device is a table lamp, or more rigorously speaking from an electromechanical standpoint, a lamp fixture. Different forms of polarity testing have different purposes. In some cases, the device to be tested will be supplying power to polarity-sensitive devices. In other cases, it is necessity to see that alternating current is connected properly to a circuit to minimize shock hazard.
The context for utilization of the present invention is found primarily in the context of testing of devices for connection to domestic current. For operation of virtually all electrical appliances other than heaving apparatus performing heating or cooing function, alternating current is supplied to homes in a two wire configuration for 110 volt service referred to as line current hereafter. The three wires are often referred to as the "plus 110 volt", ground, and "neutral" lines, with the plus and neutral lines being referred to as the "hot" lines.
Devices designed for connection to line current are configured with lines cords comprising first and second lead wires having a first end connected to a plug and a second end connected to first and second respective terminals in the device. It is desirable for best operation, and also necessary for compliance with electrical codes, that a selected one of the lead wires be connected to a hot wire, and a second of the lead wires is connected to neutral. To this end, polarized plugs are utilized in conjunction with polarized line current outlets. One blade of the plug is wider than the other, and one slot in the receptacle is wider than the other so that the plug can only have one preselected juxtaposition with the receptacle. Since a preselected plug blade can provide connection to only one wire in the receptacle, the connection of the second ends of the lead wires determines to polarity of current provided to the device. If the wires are connected in a desired, first of two possible ways to the terminals, they are said to be connected in a first polarity. If they are reversed, they are connected in a second, or wrong, polarity.
Prior art polarity testing systems to test the connection of power lines to the receptacles into which the plug will be connected are well-known in the art. In such systems, line power is connected to energize selected indicator lamps in correspondence with the polarity of power at the receptacle. These devices are suited for connection to receptacles, but not suited for connection to a power output from a connecting means, such as a lamp socket, for mechanically supporting and electrically transmitting power to an active device, such as a lamp, which connecting means is connected in series to a receptacle. U.S. Pat. No. 4,437,054 issued Mar. 13, 1984 discloses an adapter for interfacing a power receptacle polarity tester to a lamp holder. This requires the additional complexity in testing apparatus of both an adapter and a line current tester. To perform the polarity test, the lamp holder is connected to line current. This is the same line current from which t is desired to protect the ultimate user of the device. U.S. Pat. No. 4,258,313 issued Mar. 24, 1981 discloses a hand-held tool for testing lamp circuit polarity. This apparatus also contemplates connection of a device to line current while it is employed. Continuity checkers are well-known in the art, but are not configured to respond in a preselected manner to a preselected polarity and are not mechanically configured to interconnect conveniently with a socket. Significant manipulation to interface the tester to a socket may be required, leading to inefficiency and inconvenience in operation. Further, neither of these references discloses test for short circuits.